In a cloud system which is built in a datacenter, a physical server executes processing, consuming power. Virtual machines which operate in a physical server do not execute processing all the time and some virtual machines do not execute processing (that is, some virtual machines are in the idle state). Even though virtual machines which operate in a physical server are in the idle state, the physical server consumes power. Therefore, it is favorable to stop virtual machines which are in the idle state to the extent possible from the viewpoint of energy saving.
However, in the cloud system, information related to virtual machines which is available to a manager is limited. Regarding a virtual machine, it is possible for a manager to know a central processing unit (CPU) load, a memory usage rate, an input/output (I/O) load or a data transfer amount in a network, and the like, for example, but it is difficult to know whether or not a virtual machine is in the idle state. This is because information of a virtual machine is information of a user of the virtual machine and therefore, it is a problem that information of a user is available to a manager.
The following technique is widespread regarding reduction of power consumption in a cloud system. Specifically, in a system in which a plurality of blade servers are arranged, power consumption of virtual machines which operate in the blade servers is measured and the virtual machines are aggregated (that is, put together into one group) so that the power consumption does not exceed the maximum power which is set in the blade servers. Then, a blade server in which a virtual machine is not activated due to the aggregation is stopped so as to reduce power consumption of the system.
However, in this technique, it is not assumed that a virtual machine in the idle state is specified. In this technique, even virtual machines which are in the idle state are aggregated in a blade server with virtual machines which are not in the idle state. Therefore, it is difficult to stop virtual machines which are in the idle state, thus limiting the reduction amount of power consumption.
Japanese Patent No. 4488072 (corresponding to Japanese Laid-open Patent Publication No. 2009-169858) is an example of related art.